Study On Characteristics Of Three-phase AC Electroinc Load Based On Dual PWM Converter

AC electronic load is a power electronic equipment which can take place of conventional real impedance. It can be widely used in electrical laboratory, power supply manufacturer, the motor manufacturer, civil and military enterprise. The common electronic load does not simulate various characteristics of electronic load because it's unreasonable topological structure and the improper control strategy, which limit the scope of AC electronic load's application. The AC electronic load uses all-controlling power switching devices. In addition, the rectifier and the inverter are controlled by PWM technology, not only can accurately simulate all kinds of electronic load, but also the testing energy can be feedback to the utility grid. Meanwhile, the electronic load can work at different test power frequency, thus the range of electronic load is increased.Firstly, the thesis analyzes the principle of Dual-PWM converter and determines the main circuit structure of the Dual-PWM converter which consists of the PWM converter and the PWM inverter two parts. On the based of three-phase coordinate system and the rotating d-q coordinates, the thesis establishes the model and gives the design methods of the circuit parameters elaborately.Secondly, based on the topological structure of the three-phase electronic load, the thesis determines the control methods of the rectifier part and the inverter part. The rectifier part adopts double closed loop control model of the voltage and current. As a rule, the outside ring is controlled by dc voltage to stable dc voltage. On the other hand, net-side current is controlled by the circuit inside ring, which realizes net-side unit power factor and current waveform as sine. The inverter part uses the power as a control target and applies the single close-loop control method of current, which controls the outside power to dominate the phase and amplitude of the inverter to simulate various electronic loads. What's more, the energy between the load and the power translation system could be fed back. Meanwhile, the thesis gives the detailed design methods of the double closed loop control structure on the voltage and current of the PWM rectifier and the single closed-loop control structure on the current of the PWM inverter. The thesis also presents design methods of parameters about the control circuit design scheme in detail.What's more, on the based of theoretical analysis, MATLAB simulation toolbox is used to build the three-phase electronic load of the system simulation model, and the system simulation results show that the AC electronic load can accurately simulates all kinds of electronic loads include changing load, unchanging load, unbalanced load, balanced load, resistive load, capacitive load and inductive load, but also the testing energy can be feedback to the utility grid, meanwhile, those electronic load can work at different test power frequency, thus increasing the electronic load range. In a general way, the AC electronic load meets the design requirements.Finally, the method of design the AC electronic load is summarized and the next work is prospected.